From the interaction between Maleficent and the current Evil Queen it seemed like Mal was the reigning EQ before Snow White's nemesis/EQ time. In their conversation about Mal's time with Sleeping Beauty it was definitely referred to as the distant past--in fact, it seemed like quite a bit of time had passed since Maleficent had moved on (found some joy in a pet) and was apparently in semi-retirement from attempted princess homicide.
So, I guess we could deduce that it is all the same realm but perhaps the fairy tales occurred in 'real' time, that is, mirrors our concept of time progression, etc... If that is the case either this world is very large with multiple kingdoms (and a plethora of available princes) and strange (for most of the fairy tales to be occurring simultaneously) or we should see some characters that are much older, young, dead...the whole shabangabang.

